Wave plate and optical pickup unit using the same

Abstract

As a ½ wave plate constituted by laminating two wave plates, a wave plate where temperature dependence of a phase difference is reduced is provided. In a wave plate constituted by laminating a first wave plate having a phase difference τ 1 (deg.) and an optical axis azimuth θ 1 (deg.), and a second wave plate having a phase difference τ 2 (deg.) and an optical axis azimuth θ 2 (deg.), the phase difference τ 1 (deg.) of the first wave plate and the phase difference τ 2 (deg.) of the second wave plate are set to 360n+180 (n=0, 1, 2 . . . ), and an angle formed by polarization planes of incident light and emitted light is θ (deg.). In this case, the first wave plate and the second wave plate are laminated so as to satisfy θ 1 =(90+θ/2)/2 and θ 2 =θ 1 +90+θ/2.

1. A wave plate constituted by laminating a first wave plate having a phase difference τ 1  (deg.) and an optical axis azimuth θ 1  (deg.), and a second wave plate having a phase difference τ 2  (deg.) and an optical axis azimuth θ 2  (deg.), wherein when the phase difference τ 1  (deg.) of the first wave plate and the phase difference τ 2  (deg.) of the second wave plate are set to 360n+180 (n=0, 1, 2 . . . ), and an angle formed by polarization planes of incident light and emitted light is θ (deg.), the first wave plate and the second wave plate are laminated so as to satisfy θ 1 =(90+θ/2)/2 and θ 2 =θ 1 +90+θ/2. 
     
     
       2. The wave plate according to  claim 1 , wherein the first wave plate and the second wave plate are made of a crystalline board. 
     
     
       3. An optical pickup unit having the wave plate according to any one of  claim 1  and  2 .